Gee Bartram

This study reports on the first cross section measurements for the 94Sr(α, n) 97Zr and 86Kr(α, n) 89Sr reactions. In particular, our measurement of 94Sr(α, n) 97Zr is the first weak r-process reaction cross-section obtained using a radioactive ion beam. This experiment was enabled by the use of novel solid helium targets, comprised of silicon thin films with high helium incorporation obtained via a sputtering technique. Yield measurements were performed at center-of mass energies of 10.4 and 9.0 MeV for the 86Kr(α, n) 89Sr reaction, and 9.9 MeV for 94Sr(α, n) 97Zr, extending into the respective Gamow energy windows for a temperature of 5 GK. Reactions were uniquely identified by prompt γ rays detected in coincidence with heavy ions selected by a recoil mass spectrometer. The obtained cross sections are smaller than predicted for both reactions. In the case of 94Sr(α, n) 97Zr, the reaction rate found here is lowered by an order of magnitude at temperatures below 5 GK, which is expected to impact the predicted abundance of ruthenium, a signature wear-process element.